1. Field of the Invention
The present general inventive concept relates to an illuminating system designed to eliminate speckle produced by laser light and a projection system employing the same, and more particularly, to an illumination system designed to effectively reduce or eliminate laser speckle by dividing a beam emitted from a laser light source into sub-beams and temporally or spatially averaging the sub-beams and a projection system employing the same.
2. Description of the Related Art
A projection system using a laser light source provides a wide range of color rendition due to a wide color gamut while achieving high optical efficiency due to superior collimation. However, the laser-based projection system suffers from speckle due to a coherence of a laser beam. The speckle results from interference among randomly phased coherent beams reflected from a rough surface. The speckle is a main factor degrading resolution and quality of an image.
FIG. 1 illustrates a conventional illuminating device designed to eliminate laser speckle, as disclosed in U.S. Pat. No. 6,249,381. Referring to FIG. 1, in the conventional illuminating device, laser light emitted by a laser light source 10 is incident on a lens 11. Then, the laser light is condensed by the lens 11 and is incident on an incident end of an optical fiber bundle 12. The laser light is emitted through the optical fiber bundle 12 and an optical fiber 13 and illuminates a spatial modulator 15 that is a transmissive liquid crystal display through a lens 14. The conventional illuminating device further includes a projection lens 16 and a screen 17 to form an image thereon.
Since the optical fiber bundle 12 consists of a plurality of optical fibers with different lengths, a beam passing through each fiber has a different optical path length, thus contributing to a reduction in coherency of the beam.
However, since the beams passing through the optical fiber bundle 12 have different phases, the efficiency of speckle removal is degraded. Furthermore, the optical fiber bundle 12 having the optical fibers with different lengths is complicated to manufacture.